The objectives of the studies proposed here are to quantitatively determine the interaction of the carotid sinus baroreceptor reflexes with local control mechanisms, and with the aortic arch baroreceptors upon peripheral blood flow distribution in functionally different vascular beds and upon aortic hemodynamics. As these experiments are to be performed under anesthesia, the effects of the latter on carotid sinus reflex control mechanisms will be assessed initially using pentobarbital, chloralose and halothane. The interaction of the carotid sinus and local control mechanisms will be evaluated by determining regional pressure-flow relationships in vagotomized dogs with isolated, perfused carotid sinuses for the following conditions: a) variations in carotid sinus pressure with the circulation intact; b) variations in carotid sinus pressure with beds perfused at constant pressure; and c) variations in bed perfusion pressure with carotid sinus pressure constant. Values of regional vascular impedance and central hemodynamic variables will be determined at different values of mean carotid sinus pressure or bed perfusion pressure to determine the relative effects of the two factors and their interaction. Experiments are proposed in which the carotid sinuses and the aortic arch will be functionally isolated and separately perfused using controlled perfusion pressures. The effects of changes of mean pressure in one receptor area will be considered at different constant values of mean pressure in the other area and vice versa: pulsatile pressures being held constant throughout. The interaction between carotid and aortic mechanoreceptors will be established from values of regional blood flow and vascular impedance along with cardiac output, arterial pressure, and heart rate, which will be determined and represented as a family of curves versus mean pressure in the carotid sinus and/or aortic arch for various values of mean pressure in the other area. The experimental data will be evaluated by factorial analysis and analysis of variance methods. BIBLIOGRAPHIC REFERENCES: Cox, R.H. and Bagshaw, R.J.: Interaction of mean and pulsatile carotid sinus pressure in the control of regional pressure-flow relations in halothane anesthetized dogs. Fed. Proc. 36:441, 1977. Bagshaw, R.J. and Cox, R.H.: Baroreceptor control of regional hemodynamics during halothane anesthesia in the dog. Brit. J. Anesth., 1977, in press.